Resistor



Ac, c. wHl'r'rAKER HESISTOR July 22, `1941.

Filed Jan. 5, 1940 Patented `Iuly 22, 1941 aEsIs'roR Charles C. Whittaker, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 5, 1940, Serial No. 312,517

K l(Cl. 201-(58) 5 Claims.

This invention relates to electrical apparatus and particularly to resistor elements suitable for use in voltage regulators.

Another object of this invention is to provide a resistor element having discs of resistance material so arranged as to dissipate heat therefrom to maintain a substantially constant resistance under operating conditions.

A further object of this invention is to provide a resistor element having discs which are rectangular in shape and provided with a conducting oxidation resistant metallic contact surface having a lead disposed between adjacent discs in electrical Contact with their metallic surfaces and retained in assembled position under pressure whereby the element has a substantially constant electrical resistance under operating conditions.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which:

Figure 1 is a side elevational view of an embodiment of this invention, parts being broken away, r shown in section, to more clearly illustrate the invention;

Fig. 2 is a right elevational end view of the structure shown in Fig. l;

Fig. 3 is a plan view of the arrangement of the discs of the resistor element shown in Fig. 1;

Fig. 4 is a view in section greatly exaggerated showing details of a portion of the apparatus of Fig. 1, and

Fig. 5 is a diagrammatic View of the circuit and apparatus employed in a regulating system governed by the regulator shown in Fig. 1.

Referring to the drawing and particularly Fig. 1 thereof, this invention is illustrated by a plurality of elements forming a regulator which is assembled on a panel I8. As is usual practice, an electromagnet I2 having a magnetic core structure and coils vdisposed thereabout, the details of which are not shown, is mounted on the panel I0 by any suitable means not illustrated. In addition to the magnetic core structure of the electromagnet I 2, a bracket I4 is mounted on the electromagnet as by means of the screw I6, and has an upwardly projecting lug I8 formed on one end thereof to support an armature 20 of magnetic material. The armature 20 is so supported on the bracket I4 as to have a bearing point on the upwardly projecting lug I8 for permitting movement of the armature 2U under predetermined conditions as will be explained more fully hereinafter.

As illustrated, the bearing supporting the armature 20 in this embodiment comprises a leaf member 22 seating on top of the lug I8 and projecting through an opening in the armature and having one end secured to the armature as at 24. In addition to the leaf member 22, downwardly projecting leaf member 26 is provided on the face of the lug I8 for the armature to bear against, the leaf members 22 and 26 cooperating to form the pivot or bearing for the armature.

In order to prevent excessive movement of the armature 28 in a counter-clockwise direction about its bearing formed by the leaf members 22 and 26, the armature carries a lug 28 which projects outwardly therefrom and is disposed to engage a stop 38 carried by the electromagnet I2. A spring member 32 having one end secured to the leaf 22 and the other end secured to an adjustable screw 34, the details of which are well known and need not be described herein, is provided for biasing the armature 20 to its deenergized position illustrated in the drawing. The tension on the spring 32 can be adjusted lby manually adjusting the adjustable screw member 34 to vary the pull on the spring.

Since the windings of the electromagnet I2 tend to heat up when energized, a compensating device consisting of a heater 38 which is energized simultaneously with the energization of the windings of the electromagnet is mounted on the panel I0 and secured thereto in any suitable manner. Any heating condition developed in the electromagnet I2 is also developed in the heater device 36. A bimetal element 38 having one end thereof secured to a bracket 48 which, in turn, is

mounted on the panel I8 by any suitable means and having the other end secured to the adjustable screw device 34 is positioned to be directly responsive to heat radiated from the heater device 36, so that as a change in the temperature of the heater element is encountered correspond-k ing to change in temperature of the winding of the electromagnet I2, the bimetal element 38 will function to vary the pull on the spring 32, so that the bias on the armature 20 will be substantially constant for any one position of the armature 20, irregardless of the energization of the electromagnet I2.

Referring particularly to Fig. 1, a resistor element 42 is illustrated as secured to the panel I0 by means of the screws 44. This resistor element comprises a plurality of discs 46 and 48 of high resistance material such as carbon or the like assembled in a predetermined manner between two insulating plates 50 and 52. As illustrated in Fig. 3, the disks 46 and 48 are of substantially rectangular shape and are disposed in parallel planes but turned at substantially right angles to each other so as to provide projecting ends from the assembled discs. In addition to the particular arrangement of the discs shown in Fig. 3, each of the carbon discs 46 and 48 is provided with a thin iilm 54 of conducting metal which is resistant to corrosion, and particularly oxidation, such as nickel, the purpose of which will be explained more fully hereinafter. In order to provide for dividing the assembled discs into sections of equal resistance, a lead 56 comprising an extremely thin phosphor-bronze spring member is disposed between the metallic covered contact faces of adjacent disc members as illustrated in Fig. 4. In addition to the metallic film formed on the discs of high resistance material, each of the leads 56 is also coated with a thin film 58 of nickel for providing a good electrical Contact between the discs and the leads.

Referring again to Fig. l, the discs 46 and 46 of high resistance material with the leads 56 positioned therebetween are held in assembled relation between the insulating blocks 50 and 52 by means of four tie bolts 60 which are preferably enclosed in a sleeve 82 of insulating material and which extend between and project through end plates 64 and 66. These end plates are formed as part of the brackets which are mounted on the panel by the screws 44. In addition to the insulating plate 50, a pressure plate 68 is provided at one end of the assembled discs for applying pressure to the discs by adjusting the screw 'I0 which projects through the end plate 64. When the screw 'l0 is adjusted to apply pressure to the assembled discs 46 and 48 having the leads E6 therebetween, the end plates 64 and 66 function as fiat plate springs for applying pressure to the assembled discs.

Each of the spring leaves forming the leads 56 are preferably insulated from each other by layers 'li of fishpaper or other suitable insulation, shown in Fig. 5, disposed between adjacent leads. The leads 56 are positioned in a clamp assembly 12 of insulating material, the pressure of the clamp upon the leaves being adjustable by means of the screws I4. The clamp assembly l2 is suitably mounted on a base block 'i5 which is secured to the panel by means of the screw '16. Each of the leads 56 formed of the phosphor-bronze leaf spring projects downwardly from the clamp 12 and terminates adjacent a stop block 'I8 which is also secured to the base block 'l5 which carries the clamp assembly l2. At the end of each of the leaf spring members a contact button 80 of silver or the like is formed so that when adjacent contact buttons are in engagement the portion of the resistor element 42 between the leads which are in contact will be shorted. As illustrated, the stop block 'I8 is beveled to correspond to the beveled arrangement of the ends of the leads 56, so that as the leads 56 move to engage the block 18 they are permitted to separate to break any electrical contact between adjacent contact buttons 80 carried by the spring members 56. The stop block 78 is preferably adjustably mounted on the base block 'i5 to permit a certain amount of angular rocking to shift the angle of the contact or stopping surface of the stop 18 with respect to the ends of the spring members or leads 56 to permit accurate spacing of the spring members when they are biased against the stop 18. As illustrated, the armature 20 carries a member 82 which is so positioned as to engage the leaf springs or leads 56 to bias them away from the stop 18 and force the contact buttons 80 into engagement when the electromagnet I2 is deenergized.

Referring to Fig. 5, the regulator of Fig. l is illustrated in circuit with a generator, the voltage of the armature 84 of which it is desired to regulate. As illustrated, the armature 84 is connected to energize the lines 86 and 88 and has a shunt field winding 60 connected to one side of the armature 84 through the lead 92 and to the other side of the armature through the lead 94, resistor element 42, lead 96 and the junction point 98. Since it is desired that the electromagnet I2 be responsive to the voltage generated by the generator, the winding |00 of the electromagnet l2 is connected to one side of the armature 84 through the lead |02 and to the other side of the armature through the lead |04 and junction point 98. The compensating heater element 36 is likewise connected across the armature 84 by means of the leads |06 connected to the lead |02 and the lead |08 connected to the lead |04 which connects the coil of the electromagnet |2 in circuit with the generator armature.

In practice, the spring member 32 is so adjusted that when the electromagnet |2 is deenergized or when the voltage generated by the generator armature 84 is of a predetermined value, that the armature 20 is biased in a counter-clockwise direction about its bearing, so that the insulating member 82 engages the leaf springs or leads 56 to bias them away from the stop block 'i8 and force the contact buttons 80 into electrical engagement with each other to short circuit the resistor element 42 from its series circuit relation with the field winding 90. If the voltage drop across the leads 86 and 88 increases above the predetermined value, the winding |60 of the electromagnet l2 becomes sumciently energized to cause the armature 20 to rotate in a clockwise direction about its bearing against the bias of the spring 32, thereby permitting the spring leaves or leads 56 to move to the left as illustrated in Fig. 5 to progressively engage the stop block '18. At the same time that the coil |00 is energized, the heater element 36 is also energized to compensate for any change in temperature in the electromagnet |2l thereby ensuring a constant pull of the spring member 32 on the armature 20.

As the contact buttons of the spring leaves or leads 56 separate and introduce progressive amounts of the resistor element 42 starting from the right-hand side and going to the left-hand side, the excitation of the field winding 90 is reduced to effect a decrease in the voltage generated and consequently a decrease in the voltage drop across the leads 86 and 88.

As the disks of the resistor element 42 are introduced into the circuit by reason of separation of the contacts 80 of the leads 5S, it is found that considerable heat is developed in the discs of the resistor element which are introduced into the circuit. However since the discs are arranged as described hereinbefore, with the ends of the discs projecting outwardly from the stack, the heat developed within the discs of the resistor element in the circuit is efficiently dissipated by radiation from the ends of the discs. By thus arranging for the dissipation of the heat in the resistor element and since the stacked discs with the leads therebetween are maintained under a substantially uniform pressure, it is found that the resistor element has a substantially constant electrical resistance under operating conditions of the regulator.

By utilizing the hlm ci conducting non-corrosive metal nickel over the surfaces of the disks E and :it of the resistor element and over the end of each of the leads which is inserted between the adjacent discs, an extremely good electrical contact is formed between the discs of the resistor element and the leads. Further, since heat is generated within the resistor element when it is in series circuit relation with the field winding Si), the metal coating on the discs and leads prevents oxidation of the metal of the leads, thereby maintaining the contact drop between the leads and the discs substantially constant throughout the life of the element. By utilizing the resistor element formed of the plurality of discs it is evident that the total resistance oi the element or the resistance of each disc between the leads can be initiaily determined by the thickness of the discs and/or by the grade or composition of the discs. By reason oi the arrangement of the discs described hereinbefore, this resistance is substantially constant for all operating conditions of `the apparatus, the only variation being in the number of sections inserted in the circuit at any one time. Since the resistance of the element remains substantially constant when the element is used in a regulator as described hereinbefore, close control or" a generated voltage can be readily maintained.

Although this invention has been described with reference to a particular embodiment thereof, it is intended that all matters contained in the description given hereinbefore shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

l. A resistor element comprising, a plurality of rectangular discs oi resistance material dis-- posed in stacked parallel relation to form a rnain body portion, some of the discs being turned at an angle to the other discs, each of the discs having its opposite ends in a lengthwise direction projecting from opposite sides of the main body portion of the stack, a lead of goed conducting Inaterial disposed between adjacent discs and projecting outwardly therefrom, and means for scouring the stacked discs with the leads therebetween under pressure, :the projecting ends of the discs eiecting the dissipation of heat by radiation from the stack to provide a unit having a substantially constant resistance.

2. A resistor element comprising, a plurality of rectangular discs of resistance material disposed in stacked parallel relation to form a main body portion, alternate discs I" the stack being turned at substantially right angles with the ends of each of the discs in the lengthwise direction projecting from opposite sides of the main body portion of the stack, a lead of good conducting material disposed between adjacent discs and projecting outwardly therefrom, and means for securing the stacked discs in good electrical contact relation with the leads therebetween, the

projecting ends of :the discs effecting the dissipation of heat by radiation from the stack to provide a unit having a substantially constant resistance.

3. A resistor element comprising, a plurality of rectangular discs of resistance material disposed in stacked parallel relation to form a main body portion, certain of the discs having their ends in 'the lengthwise direction of the individual disc projecting outwardly from opposite sides oi the main body portion of the stack, a nlm of conducting metal kdisposed on the contacting surfaces oi the adjacent discs, a lead of good conducting material disposed between the lms of conducting metal of adjacent discs and projecting outwardly therefrom, and means for securing the stacked discs with the leads therebetween under pressure suicient to retain the leads between lthe discs in good electrical contact with the hns of conducting metal, the projecting ends of the discs effecting the dissipation of heat by radiation from the stack to provide a unit having a substantially constant resistance under operating conditions.

4. A resistor element comprising, a plurality of rectangular discs of resistance material disposed in stacked parallel relation to form a main body portion, certain of the discs having their ends in the lengthwise direction of the individual disc projecting outwardly from oppostie sides of the main body portion of the stack, a ilm of conducting metal which is resistant to oxidation disposed on the contacting surfaces of the adjacent discs as an integral part thereof, a lead of good conducting material disposed between the films of conducting metal of adjacent discs and projecting outwardly therefrom, and means for securing the stacked discs with the leads therebetween under pressure to retain the leads between the discs in good electrical contact with the films of conducting metal, the projecting ends of the discs effecting the dissipation of heat by radiation from the stack to maintain a substantially constant resistance under operating conditions.

5. A resistor element comprising, a plurality of rectangular discs of resistance material disposed in stacked parallel relation to form a main body portion, alternate discs o the stack being turned at substantially right angles with their ends in the lengthwise direction of the rectangular disc projecting outward from the opposite sides of the main body portion of the stack, a layer of conducting rnetal which is resistant to oxidation disposed on the contacting surfaces of the adjacent discs as an integral part thereof, a lead of good conducting material disposed between the layers of conducting metal of adjacent discs and projecting outwardly therefrom, and means for securing the stacked discs with the leads therebetween under pressure to retain the leads in good electrical contact with the layers of conducting metal on the discs, the projecting ends of the discs effecting the dissipation of heat by radiation from the ,stackl to substantially maintain a constant resistance under operating conditions.

CHARLES C. WHIITAKER. 

